High La site accessibility in La2O2CO3/C aerogel for advanced low-concentration phosphate removal

La-based materials are critical for mitigating eutrophication in low-phosphate aquatic environments. However, their practical application is often limited by the trade-off between high La loading and low utilization efficiency. In this study, starch is innovatively employed to immobilize La 3+ , enabling the in-situ formation of La 2 O 2 CO 3 through CO 2 gas generated during one-step pyrolysis, simultaneously, the gas expansion effect is harnessed to create a hierarchically porous architecture. The resulting La 2 O 2 CO 3 /C composite exhibits remarkable adsorption performance, achieving a phosphate uptake capacity of 306.6 mg P/g La and a P/La molar ratio of 1.37. Mechanistic studies indicate that the adsorption is predominantly driven by electrostatic interactions and ligand exchange. Theoretical calculations further reveal that the interfacial electron transfer between La 2 O 2 CO 3 and the carbon matrix enhances La adsorption activity through synergistic effects. This high site accessibility facilitates rapid phosphate diffusion and binding, thereby significantly improving La utilization efficiency. To enable practical application, the powdered adsorbent is immobilized within a chitosan/polyvinyl alcohol double-network aerogel, preserving its high performance while ensuring structural stability and recyclability. This material demonstrates robust performance in removing low-concentration phosphate, when treating real lake water, it achieves 96.8 % removal within 30 min, and in continuous-flow experiments, the cumulative treated water volume reaches 12.84 L. Furthermore, the material exhibits outstanding safety, high selectivity, and reliable reusability. This study advances the understanding of structure–performance relationships in La-based adsorbents and presents a novel design strategy for optimizing rare earth resource utilization in remediating low-concentration phosphate pollution.